Methane fluxes and isotopic composition over heterogeneous landscapes of Arctic permafrost and Siberian peatlands (MICHAEL)

北极永久冻土地貌和西伯利亚泥炭地是全球温室气体甲烷的重要来源。在气候变暖的情况下，反馈机制将进一步增加甲烷排放。然而，在俄罗斯北极和西伯利亚，只有少数几个站点可以连续测量甲烷通量，这些站点可以作为区域尺度上估计甲烷通量的参考。此外，地貌中土地覆盖的局部小规模不均一性被认为是观测到的甲烷通量不确定性的主要来源之一。甲烷通量的高时空分辨率以及热量和水分收支的高时空分辨率需要多种测量方法的结合。这种数据的缺乏限制了土地覆盖和排放模型的进一步发展。因此，Michael项目的目标是：1)除了常用的观测技术外，还利用新的观测技术提供甲烷排放、湍流热通量和同位素组成的高时空分辨率；2)通过更充分地考虑到地貌的异质性，进一步发展陆面模型和参数。选择了两个地点进行实地宣传：莱纳河三角洲的萨莫耶洛夫站和西西伯利亚中部的穆克里诺。特别关注的是小尺度的变异性和对比景观特征的影响。在项目期间，利用涡旋协方差和自动室方法获得的连续地面甲烷通量通过增加地面观测点得到加强，并结合无人驾驶航空系统对地面和气象参数、地面热平衡的组成部分、甲烷通量、甲烷浓度分布和甲烷同位素组成的测量。应用了三个无人机：一个用于包括湍流和辐射在内的气象测量的固定翼系统，一个用于获取甲烷浓度垂直分布和用于采集空气样本进行甲烷同位素组成分析的四轴飞行器，以及一个提供甲烷通量的倾斜旋翼系统。无人机在观测站周围半径长达10公里的不同位置运行，这取决于风向、大气稳定性和陆地表面，以实现足迹计算。在此基础上，对传统的涡动协方差方法和小室方法的精度进行了评估，并对升/降尺度方法进行了修正。利用数值模拟来计算排放到大气中的甲烷的三维变异性，使用陆面模拟来表示非均匀表面上的湍流交换，并使用高分辨率大气模拟来嵌入天气条件下的测量结果。一个也包含碳循环的陆面数值模型适用于所考虑的地貌。根据观测结果对模拟结果进行评估，并量化景观异质性的影响。

Arctic permafrost landscape and Siberian peatlands represent globally important sources of the greenhouse gas methane. Under warming climate, feedback mechanisms will further enhance methane emissions. However, only few sites with continuous measurements of methane fluxes are available in the Russian Arctic and Siberia, and they serve as reference for estimations on regional scales. Further, local small-scale heterogeneities of land cover within a landscape are understood to be one of the main sources of the uncertainty in the observed methane fluxes. A combination of several measurement methods for high spatio-temporal resolution of methane fluxes as well as of the heat and moisture budget is needed. This lack of data limits further land-cover and emission model development. Therefore, the project MICHAEL aims at i) providing high spatio-temporal resolution of methane emissions, of the turbulent heat fluxes and the isotopic composition using novel observational techniques in addition to those commonly used and ii) further develop land-surface models and parameterizations by taking into account landscape heterogeneities more adequately. Two sites are chosen for field campaigns: the Samoylov Station in the Lena River Delta and Mukhrino in the central part of West Siberia. The special focus is on small-scale variability and the impact of contrasting landscape features. During the project, continuous ground-based methane fluxes obtained using eddy-covariance and automatic chamber methods are enhanced with additional ground-based observational sites and combined with unmanned aerial system (UAS) measurements of surface and meteorological parameters, components of the surface heat balance, methane fluxes, profiles of methane concentration and methane isotopic composition. Three UAS are applied: a fixed-wing system for meteorological measurements including turbulence and radiation, a quadrocopter for obtaining vertical profiles of the methane concentration and for taking air samples that are analyzed for methane isotopic composition, and a tiltrotor system providing fluxes of methane. The UAS are operated at different locations within a radius of up to 10 km around the observatories, depending on wind direction, atmospheric stability and land surface to enable footprint calculations. Based on the results the accuracy of traditional eddy-covariance and chamber methods is evaluated and upscaling/downscaling methods are revised.Numerical simulations are used to derive the 3D variability of methane emitted into the atmosphere, using land-surface modelling to represent turbulent exchange over heterogeneous surface, and high-resolution atmospheric modelling to embed the measurements in the context of synoptic conditions. A numerical land-surface model containing also the carbon cycle is adapted to the considered landscapes. The modelling results are evaluated against observations and the impact of landscape heterogeneities is quantified.